The Met Office’s data from January to September 2015 already shows global average temperatures have risen by 1C for the first time compared to pre-industrial times. The rise is due to the “unequivocal” influence of increasing carbon emissions combined with the El Niño climate phenomenon currently under way. The Met Office expects the full-year temperature for 2015 to remain above 1C. It was below 0.9C in 2014, marking a sharp rise in climate terms.

“This is the first time we’re set to reach the 1C marker and it’s clear that it is human influence driving our modern climate into uncharted territory,” said Stephen Belcher, director of the Met Office’s Hadley Centre, said. “We have passed the halfway mark to the 2C target.”

The announcement of symbolic milestones in the run up to the Paris summit will increase pressure on negotiators to deliver a strong deal to avert the catastrophic global warming expected beyond 2C of warming.

“Mother Nature has been kind to the French, but it should not be that way,” said Prof Myles Allen, at the University of Oxford, referring to the impetus the milestones should give to the conference hosted in Paris. “International negotiations on climate change should not be in hoc to what happens ... in the preceding nine months.” In any case, he said: “The last three months of 2015 would have to be really odd to change [projections of unprecedented warming for 2015] as we are beating the records by a country mile.”

Amber Rudd, the UK’s energy and climate change secretary, said: “Climate change is one of the most serious threats we face, not just to the environment, but to our economic prosperity, poverty eradication and global security. That’s why I want an agreement on a global deal in Paris. Pledges to reduce emissions made by countries [are] just the beginning. We need to ensure that as the costs of clean energy fall, countries can be more ambitious with their climate targets.”

Climate change is clear in the Central England Temperature record, which is the longest in the world and stretches back to 1772, said Ed Hawkins, a climate scientist at the University of Reading. “We can see the fingerprint of global warming in our own backyard. Central England has warmed 20% more than the global average [as land warms faster than oceans] and we expect that to continue.”

The impacts of climate change are analysed in other research presented on Monday by the UK’s Avoid project. It found that, compared to unchecked global warming, keeping the temperature rise below 2C would reduce heatwaves by 89%, flooding by 76%, cropland decline by 41% and water stress by 26%.

Prof Joanna Haigh, at Imperial College London and part of the Avoid team, said the last major UN climate summit in Denmark in 2009 failed, making Paris crucial in preventing widespread damage: “Copenhagen was generally considered a complete disaster, so it is very important that countries get together at Paris.”

Belcher said 4C of warming would be much more harmful than simply doubling the impacts expected with 2C. He said the European heatwave of 2003, which led to 70,000 deaths, would be “a rather mild summer” in a 4C world.

The Met Office report also showed that the world’s “carbon budget” – the maximum CO2 that can be emitted over time to keep below 2C – was already two-thirds used up by the end of 2014. But only one-third of the sea-level rise expected from 2C of warming – 60cm by 2100 – has so far occurred, because of the time it takes for large ice sheets to melt.